Add 500 Bitbucket middleware

The middleware opens a Bitbucket issue when an error occurs.

See also https://github.com/APItools/middleware/pull/31
Merge branch '500-bitbucket-issue' of https://github.com/potomak/middleware into potomak-500-bitbucket-issue
bitbucket requres both title and content to create an issue
Merge branch 'potomak-500-bitbucket-issue'